The present invention relates to an acoustic apparatus such as a stereo acoustic system and a multi-channel acoustic system, to a method for determining a time delay of a speaker used in the acoustic apparatus, and to a recording medium.
In content such as movies recorded on a DVD (Digital Versatile Disc) and in digital television broadcast, so-called multi-channel audio data, such as a 5.1 channel and a 7.1 channel, has come to be handled, and the number of chances for a user to set a multi-channel listening system, such as a 5.1 channel and a 7.1 channel, has increased.
For example, a listening system of a 5.1 channel is formed of six audio channels: a front left channel, a front center channel, a front right channel, a back left channel, a back right channel, and a subwoofer channel, and can play back audio by using six speakers corresponding to the six audio channels. The expression [0.1] in the 5.1 channel means a subwoofer channel for compensating for low frequency components.
In a multi-channel listening system, since a plurality of speakers are used, there are cases in which a playback sound field that is formed by the multi-channel listening system does not become an appropriate one as a result of being affected by a distance between each speaker and a user, by output characteristics of each speaker, by an obstacle that exists between the speaker and the user, etc., at a position where the user listens to audio emitted from each speaker. For example, the following occurs: a sound image that should be localized at the front center is offset to the right side or to the left side.
For this reason, some multi-channel listening Systems are provided with a so-called time alignment function capable of forming an appropriate playback sound field by appropriately delaying audio emitted from each speaker. For example, a listening system 100 having a time alignment function for a speaker, shown in FIG. 15, is provided.
The listening system 100 shown in FIG. 15 allows a digital amplifier 102 to perform DAC (Digital-Analog Convert) playback of a signal for measuring a time-stretched pulse (TSP) (signal in which the energy of an impulse signal is distributed in a time axis), which is generated in a TSP signal generation section 101, and allows this signal to be emitted from a target speaker among speakers SP1 to SP5.
The TSP measurement signal emitted in this manner is collected by a microphone MC, which is arranged at a listening position selected by the user, is amplified and converted into a digital signal by a microphone amplifier+ADC (Analog-Digital Converter) 103. This signal is analyzed by a signal analysis section 104 in order to determine an impulse response.
On the basis of the determined impulse response, the time at which audio emitted from each speaker arrives at the target listening position is determined, and the delay time of the audio to be supplied to the speaker is adjusted for each speaker so that the audio from each speaker can be listened to by the user at the same timing. Thus, the optimal playback sound field corresponding to the listening position can be easily and correctly formed.
A technology used for emitting test sound from a speaker, for collecting this sound by a microphone arranged at a predetermined position, and for obtaining an impulse response as in the above-described listening system has been widely used when so-called time alignment of speakers is performed in, for example, acoustic processing apparatuses disclosed in Japanese Unexamined Patent Application Publication Nos. 10-248097 and 10-248098 (to be described later).
However, an impulse response of a subwoofer having a band of ultra-low frequencies to low frequencies among impulse responses of a plurality of speakers used to form a playback sound field with a sense of realism takes a long time until it is converged due to influences of reflection in a wall and standing waves in the case of, in particular, a room of a household. Therefore, there is a possibility that the measurement time becomes long and memory is pressed in the meaning of system implementation.
More specifically, in a multi-channel listening system, if the time delay of audio from a subwoofer speaker is to be correctly measured, problems may occur in the aspect of a processing time and manufacturing cost, such as taking a long time, and a memory having a large storage capacity for the detection of processing becoming necessary.
In view of the above, it is preferable to quickly and accurately detect a time delay with respect to audio from a speaker for low audio frequencies, such as a woofer and a subwoofer, without using a large-capacity memory.